Plant protection against insect pests is performed largely using conventional chemical insecticides. Their application is, however, problematic from nature conservation and human health points of view. Insects become more and more resistant to them which in turn leads to the increase of dosage or needs to develop other more effective insecticides. The opportunities in this direction are approaching the limits. More rigorous legislative also restrains this way of pest control.
The horse chestnut leaf miner, Cameraria ohridella (Deschka et Dimi{hacek over (c)}) (Lepidoptera: Gracillariidae) has favourable conditions for its development in the Czech Republic. This pest was discovered for the first time at Ohrid lake in Macedonia between Albania and Greece in 1984. This important pest of the horse chestnut started to spread invasively through whole Europe where it has good conditions for its development (for the lack of natural enemies) while not being enough regulated by natural mechanisms. Damage inflicted to horse chestnut leaves cause serious weakening of most of the infested trees. Contemporary pest control methods are based either on the application of non-selective insecticides or composting or burning of decaying (fallen) leaves. All these methods, however, also kill beneficial organisms including natural enemies of Cameraria ohridella. 
An application of biological control, i.e. methods based on natural antagonistic interactions between organisms for suppression of pest population is safer to natural balance and stability of agricultural and forests ecosystems. Most of these biocontrol agents are harmless for non-target organisms including man and, contrary to chemical insecticides, do not posses any ecological risk for environment and thus contribute to biodiversity conservation. For this reason, biocontrol agents are more and more preferred as alternative means of insect pest control at the global scale.
Mycoinsecticides are such means of biological control. They are based on entomopathogenic fungi. For practical pest control representatives of several key Deuteromycet (Hyphomycetes: Moniliales) are of dominant importance. The best known are entomopathogenic fungi belonging to the genera Beauveria, Hirsutella, Metarhizium, Nomuraea, Isaria (Paecilomyces), Tolypocladium and Verticillium (Lecanicillium). Among many species of these genera about 25 species are contemporarily used in the form of standard biopesticides. Application of mycoinsecticides in pest control is one of the approaches in modern applied entomology and their development reached the stage of commercial bioinsecticides in many countries.
Entomopathogenic fungus Isaria fumosorosea (syn. Paecilomyces fumosoroseus) (WIZE) Brown & Smith is in comparison to other species of entomopathogenic Deuteromycet (Beauveria bassiana, Metarhizium anisopliae, Verticillium lecanii etc.) a less studied species. Fungus Isaria fumosorosea (syn. Paecilomyces fumosoroseus), often reported under abbreviation PFR, is a cosmopolite polyphagous entomopathogenic species. Most records of the isolation of this fungus from insects (under natural conditions) frequently report species of the orders Lepidoptera, Diptera and Coleoptera as the hosts. The PFR was for the first time reported as naturally occurring pathogen in the whitefly (Trialeurodes vaporariorum) populations in Peking in 1983, where strong local epizootics occurred, which temporarily eradicated this pest. This strain of PFR was isolated and as highly virulent against greenhouse whitefly was assigned as a subspecies Paecilomyces fumosoroseus var. beijingensis. 
Substantial increase of interest in this pathogen happened when harmfulness of the whitefly Bemisia tabaci increased in field agroecosystems in Southern USA. Since 1987 regular spontaneous epizootics of Paecilomyces fumosoroseus in Bemisia tabaci populations on various host plants/localities were reported in Florida where a new strain of Paecilomyces fumosoroseus (PFR) was isolated in 1987. The isolated strain was assigned as PFR 97—strain Apopka (Apopka—name of the region in Florida. The pure culture was identified in 1988 and deposited at the American Type Culture Collection (strain ATCC 20874). Strain PFR 97 turned out to be able to cause large epizootics in Bemisia tabaci populations both in greenhouses and in the field crops. Further experiments with this strain proved the polyphagous feature of this strain and a high virulence against aphids, thrips, larvae of certain moth species, larvae and pupae of leafminers (Diptera) and even a high activity against two-spotted spider mite (Tetranychus urticae). Contrary to the fungus Verticillium lecanii, PFR is able to cause infection also in the eggs of whiteflies and spider mites.